In today's rapidly advancing semiconductor manufacturing industry, reducing device feature sizes and increasing device speed is more and more emphasized. Versatile improvement approaches are applied to manufacturing processes to gain higher device performance. For example, a single semiconductor chip may be designed to include both low resistance areas and high resistance areas. With regard to the high resistance areas, an electrostatic discharge device (ESD) may advantageously be formed to prevent from external charging damage, for example. The ESD may be achieved through applying a sacrificial covering such as an oxide layer over portions of the device to serve as a mask and prevent silicide formation in these portions.
In the semiconductor manufacturing industry, it is known that the formation of stressed films over doped areas increases the speed of the associated semiconductor device by producing a mechanical stress in the underlying film or substrate that contains the dopant impurities. Such a stress increases the mobility of the dopant impurities. The dopant impurities or charge carriers with increased mobility enable faster operating speed for semiconductor devices such as transistors. It would therefore be desirable to utilize such stressed films in various appropriate applications.
With regard to the spatially selective silicidation process, one technique is to use an oxide film as the silicide prevention film in areas that are not to be silicided. The sacrificial oxide film is patterned and removed from the areas that are to be silicided. This typically involves multiple oxide etch or strip operations. After the silicide is formed in areas where the sacrificial oxide is not present, the sacrificial oxide film must be removed from the non-silicided areas. These oxide removal operations may create voids in oxide spacers formed alongside transistor gates formed beneath the sacrificial oxide film, and may also create other divots in the device, both of which degrade device performance. Another approach is to use a stressed nitride film as a suicide prevention layer. In order to utilize a tensile or compressive stressed silicon nitride film to increase carrier mobility and also act as a silicide prevention film, a stack of a stressed nitride film over an oxide film has been tried as a suicide resistant film stack.
A shortcoming associated with the use of the nitride film, however, is that, when a stressed nitride film remains over a transistor during anneal, device degradation may occur for either or both of the PMOS and NMOS transistors, depending on the type of silicon nitride film used. Conventional techniques employing a sacrificial nitride film as part of the silicide prevention films stack may therefore adversely affect device performance of either PMOS or NMOS transistors.
As such, it would be advantageous utilize a stressed silicon nitride film as a silicidation prevention film without degrading either NMOS or PMOS device performance.